1. Field of the Invention
The present invention relates generally to a magnetic recording/playback machine and, more particularly, to an improved positioning mechanism for a read/write head for such a machine.
2. Description of the Prior Art
In recording/playback machines which utilize discs for magnetically recording information, a positioning mechanism is employed to move a head radially across concentric recording tracks on the disc surface to magnetically read or write the stored information. In some prior art mechanisms, the positioning mechanism for the magnetic read/write head includes a lead screw upon which the read/write head rides and a stepping motor by means of which the lead screw is rotationally stepped in order to advance or retract the head radially across the face of the magnetic disc. Such a mechanism inclusive of a lead screw is shown, for example, in U.S. Pat. No. 3,814,441 to Craggs. Another type of head positioning mechanism is suggested in U.S. Pat. No. 3,946,439 to Owen et al. According to that latter patent, the positioning mechanism for a read/write head includes an endless belt trained around two spaced-apart pulleys; the endless belt carries the read/write head, and one of the pulleys is driven by a stepping motor to incrementally move the belt and, hence, to advance or retract the read/write head to a position at which access is gained to information stored on a magnetic disc.
The shortcomings of the aforementioned mechanisms and similar prior art devices relate to their speed, accuracy and cost. To appreciate such shortcomings, it should initially be understood that the information on the faces of magnetic discs is stored in concentric circular tracks which are spaced apart from one another by only, say, twenty thousandths of an inch or so. Further, it should be understood that in operation a read/write head must move accurately from one track of information to another in periods of time measured in milliseconds. For such fast positioning to be realized in an accurate manner, the mass of the positioning mechanism must be quite small or else its inertia, as in the Owen et al. device, will interfere with positional accuracy. With regard to inertia, it may be realized that the greater the number of moving parts, such as pulleys or the like, which either actuate or are involved in the motion of the positioning mechanism, the greater will be the momentum of the mechanism and, hence, the more difficult to obtain quick, accurate and dependable positioning over many cycles of usage.